The endovascular treatment of a variety of vascular maladies throughout the body is an increasingly important form of therapy. Catheters have been used to place various treatment materials, devices, and drugs within arteries and veins in the human body. Examples of these vasoocclusive devices and their use in such treatments are shown in U.S. Pat. Nos. 5,234,437 to Palermo and Gia ("Detachable Pusher-Vasoocclusive Coil Assembly with Threaded Coupling") and 5,261,916 to Engelson ("Detachable Pusher-Vasoocclusive Coil Assembly with Interlocking Ball and Keyway Coupling"). These patents show methods and devices for delivery of vasoocclusive members, such as coils, or wires within the human body to sites such as aneurysms, to occlude those sites. Vasoocclusive members such as are discussed in U.S. Pat. No. 4,994,069 to Ritchart et al. may be of a regular or helical configuration or assume a random convoluted configuration at the selected site. The vasoocclusive members normally are made of a radiopaque, biocompatible metal such as platinum, gold, tungsten, or alloys of these and other metals.
In treating aneurysms, it is common to place one or more vasoocclusive members within the aneurysm. The vasoocclusive members occlude the site by posing a physical barrier to blood flow and by promoting thrombus formation at the site.
Vasoocclusive members have typically been placed at the desired site within the vasculature using a catheter and a pusher. The site is first accessed by the distal end of a catheter. In treating peripheral or neural conditions requiring occlusion, the sites are accessed with flexible, small diameter catheters such as those shown in U.S. Pat. Nos. 4,739,768 to Engelson and 4,813,934 to Engelson and Daniels. The catheter may be guided to the site through the use of guidewires (see U.S. Pat. No. 4,884,579 to Engelson) or by flow-directed means such as balloons placed at the distal end of the catheter. Use of guidewires involves the placement of relatively long, torqueable proximal wire sections within the catheter, which proximal sections are attached to more flexible distal end wire section designed to be advanced across sharp bends at vessel junctions. The guidewire is visible using x-ray and allows a catheter to be manipulated through extremely tortuous vessels, even when such vessels are surrounded by soft tissue such as the brain.
Once the selected site has been reached, the catheter lumen is cleared by removing the guidewire (if a guidewire has been used), and the vasoocclusive member is placed into the proximal open end of the catheter and advanced through the catheter with a pusher. Pushers are wires having a distal end that is adapted to engage and push the vasoocclusive member through the catheter lumen as the pusher is advanced through the catheter. When the vasoocclusive member reaches the distal end of the catheter, it is discharged from the catheter by the pusher into the vascular site. This technique of discharging the vasoocclusive member from the distal end of the catheter has a number of undesirable limitations. First, because of the plunging action of the pusher and the vasoocclusive member, the positioning of the vasoocclusive member at the site cannot be controlled to a fine degree of accuracy. Second, once the vasoocclusive member has left the catheter, it is difficult to reposition or retrieve the vasoocclusive member if such is desired. Nevertheless, the technique has the benefit of delivering multiple vasoocclusive members at low cost with a short delivery time.
Several classes of techniques have been developed to enable more accurate placement of vasoocclusive members within a vessel. One class involves the use of electrolytic means to detach the vasoocclusive member from the pusher. In one technique (U.S. Pat. No. 5,122,136 to Guglielmi et al.) the vasoocclusive member is bonded via a metal-to-metal joint to the distal end of the pusher. The pusher and vasoocclusive member are made of dissimilar metals. The vasoocclusive member-carrying pusher is advanced through the catheter to the site and a low electrical current is passed through the pusher-vasoocclusive member assembly. The current causes the joint between the pusher and the vasoocclusive member to be severed via electrolysis. The pusher may then be retracted leaving the detached vasoocclusive member at an exact position within the vessel. In addition to enabling more accurate vasoocclusive member placement, the electric current may facilitate thrombus formation at the vasoocclusive member site. The only perceived disadvantage of this method is that the electrolytic release of the vasoocclusive member requires a period of time so that rapid detachment of the vasoocclusive member from the pusher does not occur. Other examples of this technique can be found in U.S. Pat. No. 5,423,829 to Pham et al. and U.S. Pat. No. 5,522,836 to Palermo.
Other forms of energy are also used to sever sacrificial joints that connect pusher and vasoocclusive member apparatus. An example is that shown in Japanese Laid-Open Patent Application No. 7-265431 or corresponding U.S. Pat. No. 5,759,161 to Ogawa et al. A sacrificial connection member, preferably made from polyvinylacetate (PVA), resins, or shape memory alloys, joins a conductive wire to a detention member. Upon heating by a monopolar high frequency current, the sacrificial connection member melts, severing the wire from the detention member.
In U.S. Pat. No. 4,735,201 to O'Reilly, an optical fiber is enclosed within a catheter and connected to a metallic tip on its distal end by a layer of hot-melt adhesive. The proximal end of the optical fiber is connected to a laser energy source. When endovascularly introduced into an aneurysm, laser energy is applied to the optical fiber, heating the metallic tip so as to cauterize the immediately surrounding tissue. The layer of hot-melt adhesive serving as the bonding material for the optical fiber and metallic tip is melted during this lasing, but the integrity of the interface is maintained by application of back pressure on the catheter by the physician. When it is apparent that the proper therapeutic effect has been accomplished, another pulse of laser energy is then applied to once again melt the hot-melt adhesive, but upon this reheating the optical fiber and catheter are withdrawn by the physician, leaving the metallic tip in the aneurysm as a permanent plug.
Another class of techniques for placing and detaching an embolic vasoocclusive member at a therapeutic site involves the use of mechanical attachment and release mechanisms, such as that shown in U.S. Pat. No. 5,261,916 to Engelson. In that technique, a vasoocclusive member having an enlarged portion is mated with a pusher having a keyway adapted to receive the enlarged portion of the vasoocclusive member in an interlocking relationship and covered by a coaxial member about the pusher and the vasoocclusive member. The coaxial member is movable by sliding the member axially. As the coaxial member is moved away from the junction where the vasoocclusive member's member engages the member of the keyway of the pusher, the vasoocclusive member disengages and the pusher is removed.
U.S. Pat. No. 5,304,195 to Twyford, Jr. et al. discloses a variation in which a vasoocclusive member and a pusher are each supplied with a ball on their proximal and distal ends, respectively. The portion of the vasoocclusive member and pusher containing the ball are radially biased and shaped to overlap each other so that when coupled, they maintain an interlocked position when enclosed within a coaxial sleeve. When the sleeve is retracted at the therapeutic site, the balls are allowed to move radially relative to one another to disengage and uncouple the pusher and vasoocclusive member.
In U.S. Pat. No. 5,350,397 to Palermo et al., a similar device is disclosed in which an embolic vasoocclusive member having an enlarged member, such as a ball, is released from a pusher assembly by forcing the enlarged member through an aperture in a socket situated on the distal end of a pusher assembly.
Another device for placement of vasoocclusive members is shown in U.S. Pat. No. 5,234,437 to Sepetka. This device includes a vasoocclusive member having a helical portion at one end and a pusher which is threaded to the inside of the helical vasoocclusive member by the use of a threaded section on the outside of the pusher. The device operates to release the vasoocclusive member by engaging the proximal end of the vasoocclusive member with a sleeve while the pusher is unthreaded. Once the pusher is free, the sleeve may be used to push the vasoocclusive member out into the treatment area.
U.S. Pat. No. 5,250,071 to Palermo discloses a vasoocclusive member and pusher assembly in which two interlocking clasps serve as a mechanical junction for the vasoocclusive member and pusher. The clasps may be supplied with apertures centrally aligned with the vasoocclusive member lumen for a control wire which, when axially withdrawn from the junction at the therapeutic site by the physician, leave the interlocking clasps free to separate, placing the vasoocclusive member at the desired therapeutic site. Alternatively, as shown in U.S. patent application Ser. No. 08/331,360, filed Dec. 21, 1994, similar self-disengaging interlocking clasps without such a control wire may be kept together by the catheter walls until released from the catheter; at that point, a simple twisting motion, gravity, fluid flow, or a combination thereof supplies the necessary force to uncouple the clasps.
The junction created by these mechanical attachment and release mechanisms is typically separable with some ease, i.e., usually by withdrawing a control wire, utilizing the built-in radial bias of the connecting members, torquing or unscrewing, or allowing gravity or fluid flow to facilitate separation in the case of self-disengaging clasps. It can still be difficult, however, to precisely control the exact moment at which that junction is separated, and premature separation due in part to a lack of adequate friction is always a possibility. In addition, those devices in which the junction is composed entirely of a either a sacrificial material, such as that taught by Japanese Laid-Open Patent Application No. 7-265431 or corresponding U.S. Pat. No. 5,759,161 to Ogawa et al, or an adhesive, such as the hot-melt adhesive disclosed in U.S. Pat. No. 4,735,201 to O'Reilly, may be prone to reliability problems as the security of a mechanically interlocking or attachable clasp or other mechanism is absent.
Accordingly, none of these disclosed devices teaches or suggests a vasoocclusive member assembly having a friction-enhancing mechanical detachment junction by the addition of a thermoplastic member that does not soften until radio frequency energy is administered to the assembly. This combination allows for improved reliability and a higher degree of control over the release of the vasoocclusive member into the therapeutic site without sacrificing the integrity intrinsic to a mechanical detachment junction.